The present invention relates to an injector for controlling fluids having a hydraulic pressure intensifier and a priming device to replace the fluid loss caused by leakage at the hydraulic pressure intensifier. In particular the present invention relates to an injector having a piezoelectric actuator for a pressure-controlled common-rail system.
In fuel injection systems with piezoelectric actuators, a control valve controlling the movement of the injector needle is often controlled through a hydraulic pressure intensifier rather than directly. The function of this hydraulic pressure intensifier is on the one hand to intensify the stroke of the piezoelectric actuator and on the other to isolate the control valve from any static thermal expansion of the actuator during operation. In order for the hydraulic pressure intensifier to operate accurately, it must always be completely full, since otherwise the stroke of the piezoelectric actuator would not be intensified, or would be intensified only incompletely. Since at every actuation of the hydraulic pressure intensifier a portion of the fluid (generally fuel) present in the hydraulic pressure intensifier is lost by leakage through clearances, it must be refilled between each injection. This re-filling can, for example, be implemented by using an appropriate arrangement of throttles by which the rail pressure of the system is throttled and tapped off in order to prime the hydraulic pressure intensifier. In that operation, the priming pressure may be dependent on the rail pressure or may be kept constant by a suitable non-return valve.
The type of priming described above, however, gives rise to several problems. On one hand, the arrangement as described results in permanent leakage, which adds to the leakage caused by the actuation of the hydraulic pressure intensifier to increase the total leakage. The result is a drop in efficiency of the injection. Furthermore, such an arrangement is comparatively expensive, since it requires a filter in order to prevent the ingress of dirt which would cause blocking of the hydraulic pressure intensifier. In addition, the throttles for throttling the rail pressure have to be made extremely accurately, in order to permit precise priming of the hydraulic pressure intensifier. As a result, the known priming device becomes very expensive.
The injector according to the present invention for controlling fluids has the advantage over the related art that the priming of a pressure chamber of the hydraulic pressure intensifier takes place simultaneously with the return of the hydraulic pressure intensifier to its starting position. In that operation, a first piston of the hydraulic pressure intensifier creates a displacement effect in a priming chamber of a priming device, either directly or indirectly. As a consequence of the return of the first piston, fluid is displaced from the priming chamber and directed to the pressure chamber of the hydraulic pressure intensifier, in order to compensate for the leakage losses which have occurred there. By this approach, according to the present invention a particularly simple and compact priming device can be created, having only a small number of components, in particular since the first piston of the hydraulic pressure intensifier can be used as the actuating member of the priming device. In addition, in a device according to the present invention no additional leakage losses occur. According to the present invention a priming pump integrated in the injector is provided for the hydraulic pressure intensifier, this pump having a minimum number of components and refilling the pressure chamber every time that the hydraulic pressure intensifier is returned. In this way, the pressure chamber is constantly filled, in preparation for every injection.
In order to create a particularly compact priming device, the priming chamber of the priming device is advantageously situated directly at the end of the first piston facing the piezoelectric actuator. Thereby the first piston is able to displace fluid directly from the priming chamber as it returns to its starting position and thus compensate for the leakage losses in the pressure chamber.
In order to make the priming chamber simple to produce, it is advantageous if it is formed in an annular shape.
According to another preferred embodiment of the present invention the priming chamber is surrounded by a primer housing. In a particularly advantageous embodiment the priming chamber is formed as a recess in the primer housing.
According to a further preferred embodiment of the present invention the first piston is situated in a cylinder-ring-shaped sleeve.
It is advantageous if the return of the hydraulic pressure intensifier is brought about by a spring component situated between the piezoelectric actuator and the hydraulic pressure intensifier.
In a particularly advantageous embodiment, the spring component is supported by the primer housing. As a result, the spring component simultaneously also provides a seal between the primer housing and the cylindrical sleeve of the first piston.
It is advantageous if an intermediate piston is situated between the piezoelectric actuator and the first piston, on which a disk-shaped element is situated. The disk-shaped element is designed in the form of a seat for the spring component. As a result, the hydraulic pressure intensifier is returned via the disk-shaped element and the intermediate piston, which is rigidly connected to the first piston.
In a particularly advantageous embodiment, the disk-shaped element is formed as a snap ring, which is situated in a slot formed in the intermediate piston. This makes it possible for the construction to be particularly simple.
It is advantageous if a fluid leak duct is provided in the area of the first piston in order to remove the leaked fluid from the hydraulic pressure intensifier.
The injector according to the present invention can be used particularly advantageously with accumulator-type fuel injection systems such as the common-rail system.